Rotating blowout preventors form a critical part of a tool string for the reason that mud is circulated into and out of the borehole in conjunction therewith and accordingly, it is important that the rotating blowout preventor be able to function properly under continuous duty for several weeks while a borehole is being formed.
In drilling deep wells it is extremely expensive to shut a rig down and therefore great emphasis is placed upon the ability to field repair or field replace equipment, such as blowout preventors, at the drilling rig with a minimum of down time being involved.
Rotating blowout preventors of the prior art generally require that the entire assembly be lifted in a telescoping manner free of the turn table and kelly in order to replace any component parts thereof including the stripper rubber or stripper seal. Should the bearings or seals require servicing, it is generally necessary to carry the rotating blowout preventor into a service shop and accordingly, a considerable amount of down time is involved before the drilling operation can be resumed.
Accordingly, it would be desirable to be able to replace the stripper rubber or the stripper seal associated therewith without having to remove the entire rotating blowout preventor from the tool string. It would furthermore be desirable to be able to replace the bearings and bearing seals thereof without having to unbolt the massive blowout preventor and transport the blowout preventor to a service shop. More especially it would be desirable to have a rotating blowout preventor which normally could endure the abuse of drilling an entire borehole before the apparatus requires servicing.
It would also be desirable to have made available a rotating blowout preventor which eliminates the troublesome kelly drive bushing.
These desirable attributes are the subject of the present invention.